Integrated optical structures with electrically conductive parts

ABSTRACT

The invention concerns a integrated optical structure comprising a plurality of parts made at least of a dielectric material, stacked according to the levels of integration and defining at least an optical microguide, and further comprising at least an integrated part ( 15 ) made of an electrically conductive material, interposed or inserted between at least two of said dielectric parts and having at least one part ( 11   a ) externally accessible to said dielectric parts for at least an external electrical connection.

[0001] The present invention relates to the field of integrated opticalstructures.

[0002] In general, an integrated optical structure comprises amultiplicity of parts made of dielectrics, these being stacked in levelsof integration and defining integrated optical microguides for thetransmission, conversion or treatment of light waves.

[0003] Certain integrated optical structures furthermore have metallicsurface regions that are connected via metal wires, constituting wirebridges, to an electrical control or supply source. This is inparticular the case in integrated optical structures that includeactuators composed of combs lying in a cavity and having tines lyingalong and at a certain distance from fixed surfaces, said metallicregions extending along the lateral faces of the tines and along thefixed surfaces so as to constitute comb displacement electrodes.

[0004] Such arrangements have the following main drawbacks. Theoperations of mounting the electrical connection wires aretime-consuming and tedious, and must be carried out accurately. Theseelectrical connection wires project from the surface of the opticalstructures and there is a risk of them touching one another.

[0005] The object of the present invention is to improve integratedoptical structures so as to facilitate and improve the electricalconnections of functional parts of such structures that require a powersupply.

[0006] The integrated optical structure according to the inventioncomprises a multiplicity of parts made of at least one dielectric, thatare stacked in levels of integration and define at least one opticalmicroguide.

[0007] According to the invention, this structure furthermore includesat least one conducting integrated part made of an electricallyconducting material, that is interposed or inserted between at least twoof said dielectric parts, and at least one connection part made of anelectrically conducting material, externally accessible to saiddielectric parts for the purpose of making at least one externalelectrical connection to this conducting integrated part.

[0008] The integrated structure according to the invention comprises atleast two groups of electrically conducting regions produced in onelevel of integration.

[0009] According to the invention, at least one conducting integratedpart includes at least one main part lying in a different level ofintegration from that of said groups and crossing at least oneconducting region of one of said groups and secondary parts lyingperpendicular to the planes of integration and connecting this main partand the conducting regions of the other group.

[0010] According to the invention, at least two conducting integratedparts may advantageously comprise at least one main part lying in atleast one level of integration and secondary parts, respectively, whichconnect their main parts and the metal regions of said groups,respectively.

[0011] According to the invention, at least one of said upper conductingregions preferably includes at least one part constituting an electrode.

[0012] The integrated structure according to the invention mayadvantageously include a moveable member provided with at least oneelectrode located opposite, and at a certain distance from andelectrically coupled to, said part, constituting an electrode so as toform an optical actuator.

[0013] According to the invention, said moveable member mayadvantageously carry at least one optical microguide.

[0014] According to the invention, at least one conducting integratedpart preferably includes at least one main part lying in one level ofintegration and, at least at one point in this main part, a secondarypart lying perpendicular to the planes of integration and passingthrough at least one dielectric part adjacent to this point.

[0015] According to the invention, at least one secondary partpreferably constitutes an external electrical connection part.

[0016] According to the invention, at least two conducting integratedparts preferably include main parts lying in different levels ofintegration.

[0017] According to the invention, said conducting integrated partspreferably include main parts that intersect at a point and at least onesecondary part lying perpendicular to the planes of integration andpassing through the dielectric part or parts separating said main partsat this point so as to connect these main parts.

[0018] According to the invention, at least one conducting integratedpart preferably includes at least one integrated main part constitutingan electrical resistor lying along and in the vicinity of one part of anintegrated microguide and secondary parts that are externallyaccessible, for the purpose of making an external electrical connectionto this main part.

[0019] According to the invention, said electrical resistor ispreferably a resistance heating element.

[0020] According to the invention, said electrical resistor mayadvantageously be a temperature measurement resistor.

[0021] According to another embodiment of the invention, at least oneconducting integrated part may advantageously include at least oneintegrated main part constituting an electrical resistor lying along andin the vicinity of one part of an integrated microguide and secondaryparts that are externally accessible, for the purpose of making anexternal electrical connection to this main part.

[0022] According to the invention, said electrical resistor may be aresistance heating element.

[0023] According to the invention, said electrical resistor may be atemperature measurement resistor.

[0024] The present invention will be more clearly understood onexamining integrated optical structures that are described by way ofnon-limiting examples and illustrated by the drawing in which:

[0025] FIGS. 1 to 6 show, in section, an integrated optical structureaccording to the present invention, in its successive fabrication steps;

[0026]FIG. 7 shows a top view of another integrated optical structureaccording to the present invention;

[0027]FIG. 8 shows a cross section on VIII-VIII of the integratedoptical structure of FIG. 7;

[0028]FIG. 9 shows a cross section on IX-IX of the integrated opticalstructure of FIG. 7;

[0029]FIG. 10 shows a cross section on X-X of the integrated opticalstructure of FIG. 7;

[0030]FIG. 11 shows a cross section of another integrated opticalstructure according to the present invention;

[0031]FIG. 12 shows a horizontal section on XII-XII of the integratedoptical structure of FIG. 11; and

[0032]FIG. 13 shows, in section, an alternative embodiment of theintegrated optical structure of FIGS. 1 to 6.

[0033]FIG. 1 shows an integrated optical structure 1 in the course offabrication, which comprises a support wafer 2, for example made ofsilicon, on one face of which a layer 3 made of a dielectric orelectrically nonconducting material, for example undoped silica, isdeposited.

[0034] Next, a layer 4 made of an electrically conducting material, forexample polycrystalline silicon, titanium, titanium nitride or tungsten,is deposited. Depending on predetermined requirements, one or moreconducting tracks or regions 5 are then produced, using aphotolithography and etching process, by removing the material of thelayer external to these regions 5.

[0035]FIG. 2 shows how the process continues with the deposition of alayer 6 of a dielectric or electrically nonconducting material, forexample doped silica, silicon nitride or silicon oxynitride. The layer 6is such that the conducting tracks or regions 5 produced above arecovered.

[0036] After optional planarization of the surface of the layer 6, alayer 7 made of an electrically conducting material, for examplepolycrystalline silicon, titanium, titanium nitride or tungsten, isdeposited.

[0037] One or more conducting tracks or regions 8 are then producedusing a photolithography and etching process, by removal of the materialof the layer 7 external to these regions 8.

[0038] Referring to FIG. 3, an optical wave transmission core 9 a ofsquare or rectangular cross section is then produced in the dielectriclayer 6 using a photolithography and etching process, by removal of thematerial of this layer 6 on either side of this core, this operationbeing carried out in such a way that the transmission core 9 a has apredetermined design or path.

[0039] Of course, during the design of the optical structure 1, thenonconducting tracks or regions 5 and 8 are preferably arranged so as tobe located laterally to and at a certain distance from the transmissioncore 9 a to be obtained.

[0040] Next, as shown in FIG. 4, a layer 10 of a dielectric orelectrically nonconducting material, for example undoped silica, isdeposited. This layer 10 fills the spaces left on either side of thetransmission core 9 a produced in the layer 6 and covers the conductingregions or tracks 8.

[0041] As a result, the transmission core 9 a and the layers 3 and 10that surround it define an integrated optical microguide 9.

[0042] Next, as shown in FIG. 5, holes or wells 11, passing through thedielectric layers 6 and 10 and emerging at points located above theconducting tracks or regions 5, and holes or wells 12, passing throughthe layer 10 and emerging at points located above the conducting regionsor tracks 8, are produced, for example using a photolithography andetching process.

[0043] Finally, as shown in FIG. 6, a layer 13 made of an electricallyconducting material, for example polycrystalline silicon, titanium,titanium nitride, tungsten or aluminum, is deposited, this materialfilling the holes or wells 11 and 12 so as to constitute interconnectvias 11 a and 12 a.

[0044] Next, using a photolithography and etching process, upperconducting regions 14 are produced by removal of the material of thelayer 13 external to these regions, these conducting regions 14 lyingrespectively above at least one of the holes or wells 11 and 12 producedbeforehand and filled by the interconnect vias 11 a and 12 a.

[0045] As a result of the foregoing operations, the integrated opticalstructure 1, as shown in definitive form in FIG. 6, compriseselectrically conducting integrated parts 15 that have main partsconsisting of the conducting tracks or regions 5 produced in the planeof integration subjacent to the transmission core 9 a and secondaryparts consisting of the interconnect vias 11 a formed perpendicularly tothis plane of integration, respectively, and electrically conductingintegrated parts 16 that have main parts consisting of the conductingtracks or regions 8 produced in the plane of integration subjacent tothe upper layer 10 and secondary parts consisting of the interconnectvias 12 a formed perpendicular to this plane of integration,respectively.

[0046] The interconnect vias 11 a and 12 a are accessible externally tothe structure 1, the upper conducting regions being produced so as tomake it easier for external electrical connections to the integratedconducting parts 15 and 16 and/or so as to produce, according topredetermined requirements, selective electrical interconnects betweenthese integrated conducting parts.

[0047] In the example shown in FIG. 6, the integrated optical structure1 is such that the conducting integrated parts 15 and 16 are placed asufficient distance from the transmission core 9 a of the opticalmicroguide 9 so as not to disturb the propagation of the optical wave inthis transmission core 9 a.

[0048] In an alternative embodiment, the conducting regions or tracks 5and 7 could be formed in trenches provided in the dielectric layers 3and 6 after chemical-mechanical polishing of the conducting layers 4 and7 that fill these trenches.

[0049] Referring to FIGS. 7 to 10, an integrated optical structure 100will now be described that implements in one particular way thearrangements described with reference to FIGS. 1 to 6.

[0050] The optical structure 100 comprises, as in the previous example,a support wafer 101 corresponding to the support wafer 2 and, insuccession, three layers 102, 103 and 104 corresponding to the layers 3,6 and 10.

[0051] The structure 100 has a cavity 105 hollowed out through thelayers 102, 103 and 104 and into the support wafer 101, said cavityhaving two parallel walls 105 a and 105 b, an end wall 105 c and abottom 105 d.

[0052] The cavity 105 is produced so as to form an actuator 106 thatcomprises a moveable member 107 free underneath and having a main branch108, that extends parallel to the walls 105 a and 105 b, and, on eachside of this main branch 108, spaced-apart transverse secondary branches109 and 110, and also fixed parts 111 and 112 that project from thewalls 105 a and 105 b, and the sidewalls or lateral faces of which lieparallel to and a certain distance from the sidewalls or lateral facesof the secondary branches 109 of the moveable member 107.

[0053] The upper face of the moveable member 107 and the sidewalls orlateral faces of its secondary branches 109 and 110 are covered with acoating of an electrically conducting material 113 so as to constituteelectrodes.

[0054] The opposed sidewalls or lateral faces of the fixed parts 111 and112 and the upper face of these projecting parts 111 and 112 areprovided with coatings 114 and 115 made of an electrically conductingmaterial respectively, these being electrically isolated from each otherso as to constitute independent electrodes. These coatings 114 and 115extend beyond the projecting parts 111 and 112 on the upper face of thelayer 104 so as to constitute independent electrically conducting upperregions 116 and 117.

[0055] The upper face of the layer 104 furthermore carries coatings 118and 119 made of a conducting material which run along at a certaindistance from the end wall 105 c of the cavity 105.

[0056] The optical structure 10 includes, on either side of and at acertain distance from the cavity 105, the integrated conducting parts120 and 121 that correspond to the integrated conducting parts 15 and 16of the example described with reference to FIG. 6.

[0057] As shown in FIG. 9, the integrated conducting parts 120 compriseintegrated main parts or tracks 122 and interconnect vias 123 that areformed below the upper conducting regions 116 and the upper conductingregion 118, respectively. Thus, all the corresponding electrodes 114 areelectrically connected together.

[0058] Likewise, as shown in FIG. 10, the integrated conducting parts121 comprise integrated main parts or tracks 124 and interconnect vias125 that are formed below the upper conducting regions 116 and the upperconducting region 118, respectively. Thus, all the correspondingelectrodes 115 are electrically connected together.

[0059] It is then possible to connect all the electrodes 114 and all theelectrodes 115 to a power supply solely by two electrically conductingwires 126 and 127 that are soldered to one of the upper conductingregions 116 and 117 or to the upper conducting regions 118 and 119,respectively.

[0060] By supplying power to the electrodes 113 of the moveable member107 via electrical connection means (not shown) such as an electricalwire and by supplying power selectively to the electrodes 113, by meansof the electrical wires 127 and 128, the moveable member 107 of theactuator 106 can be displaced parallel to its main branch 108 in onedirection or the other.

[0061] In one example, the moveable member 107 of the actuator 106 maybe connected to a beam or to an optical switching platform carrying oneor more optical microguides as described in patents FR-A-90/03902 andFR-A-95/00201.

[0062]FIGS. 11 and 12 show an integrated optical structure 200 thatcomprises a Mach-Zehnder interferometer 201 formed by an inputmicroguide 202, an output microguide 203 and two microguides 204 and 205that connect the microguides 202 and 203 in parallel.

[0063] The optical structure 200 furthermore includes an electricallyconducting integrated part 206 produced like the integrated conductingpart 15 described with reference to FIG. 6.

[0064] This integrated conducting part 206 comprises a main part 207,that is produced in the plane of integration of the aforementionedoptical microguides and lies along and a short distance from the opticalmicroguide 205, and two interconnect vias 208 and 209 for electricallyconnecting the ends of the conducting main part 207 to an external powersupply.

[0065] The main part 207 of the integrated conducting part 206 may thenform a resistance heating element capable of varying, by thermalconduction, the temperature of the optical microguide 205 in such a waythat the Mach-Zehnder interferometer 201 can form an optical switch, anoptical attenuator or an optical interrupter.

[0066] According to another embodiment, the main part 207 of theintegrated conducting part 206 could be used for the purpose ofmeasuring the temperature of the structure in its environment.

[0067]FIG. 13 shows an integrated optical structure 300 that differsfrom the integrated optical structure 1 described with reference toFIGS. 1 to 6 by the fact that, before the conducting layer 7 isdeposited on the dielectric layer 6 at least one hole 301 is made inthis dielectric layer 6 above at least one conducting track or region 5.

[0068] As the conducting layer 7 is being deposited, the material ofwhich it is composed fills the hole 301 and constitutes an interconnectvia 301 a.

[0069] During the step of etching the conducting layer 7, a track orregion 8 is produced above the hole 301 and is electrically connected tothe track or region 5 beneath the interconnect via 301 a.

[0070] Thus, electrical connections between levels may be produced.

[0071] The present invention is not limited to the examples describedabove. Many alternative embodiments are possible without departing fromthe scope defined by the appended claims.

1. An integrated optical structure comprising a multiplicity of partsmade of at least one dielectric, these being stacked in levels ofintegration and defining at least one optical microguide and at leastone conducting integrated part made of an electrically conductingmaterial, that is interposed or inserted between at least two of saiddielectric parts, and at least one connection part made of anelectrically conducting material, connected to said conductingintegrated part and externally accessible to said dielectric parts forthe purpose of making at least one external electrical connection tothis conducting integrated part, characterized in that it comprises atleast two groups of electrically conducting regions (116; 117) producedin one level of integration and in that at least one conductingintegrated part (121) includes at least one main part (124) lying in adifferent level of integration from that of said groups and crossing atleast one conducting region (116) of one of said groups and secondaryparts (125) lying perpendicular to the planes of integration andconnecting this main part (124) and the conducting regions (117) of theother group.
 2. The structure as claimed in claim 1, characterized inthat at least two conducting integrated parts (120; 121) comprise atleast one main part (122; 124) lying in at least one level ofintegration and secondary parts (123; 125), respectively, which connecttheir main parts (122; 124) and the metal regions (116; 117) of saidgroups, respectively.
 3. The structure as claimed in claim 1,characterized in that at least one of said upper conducting regions(116; 117) includes at least one part (114; 115) constituting anelectrode.
 4. The structure as claimed in claim 3, characterized in thatit includes a moveable member (107) provided with at least one electrodelocated opposite, and at a certain distance from and electricallycoupled to, said part (114; 115), constituting an electrode so as toform an optical actuator (106).
 5. The structure as claimed in claim 4,characterized in that said moveable member (107) carries at least oneoptical microguide.
 6. The structure as claimed in claim 1,characterized in that at least one conducting integrated part (15)includes at least one main part (5) lying in one level of integrationand, at least at one point in this main part, a secondary part (11 a)lying perpendicular to the planes of integration and passing through atleast one dielectric part adjacent to this point.
 7. The structure asclaimed in claim 1, characterized in that at least one secondary part(11 a) constitutes an external electrical connection part.
 8. Thestructure as claimed in claim 1, characterized in that at least twoconducting integrated parts (15; 16) include main parts (5; 8) lying indifferent levels of integration.
 9. The structure as claimed in claim 8,characterized in that said conducting integrated parts include mainparts that intersect at a point and at least one secondary part lyingperpendicular to the planes of integration and passing through thedielectric part or parts separating said main parts at this point so asto connect these main parts.
 10. The structure as claimed in claim 1,characterized in that at least one conducting integrated part (206)includes at least one integrated main part (207) constituting anelectrical resistor lying along and in the vicinity of one part of anintegrated microguide (205) and secondary parts (208, 209) that areexternally accessible, for the purpose of making an external electricalconnection to this main part.
 11. The structure as claimed in claim 10,characterized in that said electrical resistor is a resistance heatingelement.
 12. The structure as claimed in claim 10, characterized in thatsaid electrical resistor is a temperature measurement resistor.
 13. Anintegrated optical structure comprising a multiplicity of parts made ofat least one dielectric, these being stacked in levels of integrationand defining at least one optical microguide and at least one integratedpart made of an electrically conducting material, that is interposed orinserted between at least two of said dielectric parts, and at least oneconnection part made of an electrically conducting material, connectedto said conducting integrated part and externally accessible to saiddielectric parts for the purpose of making at least one externalelectrical connection to this conducting integrated part, characterizedin that at least one conducting integrated part (206) includes at leastone integrated main part (207) constituting an electrical resistor lyingalong and in the vicinity of one part of an integrated microguide (205)and secondary parts (208, 209) that are externally accessible, for thepurpose of making an external electrical connection to this main part.14. The structure as claimed in claim 13, characterized in that saidelectrical resistor is a resistance heating element.
 15. The structureas claimed in claim 13, characterized in that said electrical resistoris a temperature measurement resistor.
 16. The structure as claimed inclaim 2, characterized in that at least one of said upper conductingregions (116; 117) includes at least one part (114; 115) constituting anelectrode.
 17. The structure as claimed in claim 16, characterized inthat it includes a moveable member (107) provided with at least oneelectrode located opposite, and at a certain distance from andelectrically coupled to, said part (114; 115), constituting an electrodeso as to form an optical actuator (106).